using AC power for piezo buzzer

[Matt]

1. We dont know exactly what the OP is doing. This buzzer may well be
run via a separate doorbell switch from the main electromechanical
bell. If so, the buzer, being relatively low consumption, will see more
or less unloaded voltage, ie well above 12.8.

2. If the buzzer is parallelled with the existing doorbell, again we
dont know what the bell design is. Last electromechanical one I had
used a mercury switch and a solenoid to bang back and forth between 2
ding-bars. This means the current draw was being switched on-off-on-off
while in use. So again the buzzer is liable to see unloaded transformer
voltage.

So I think we really can not assume either way, and need to design
soemthing that will work either way.

You could ask . If it wasn't clear from my previous posts, I intend
to take power right off the contacts of the solenoid of the existing
bell.

I'll try to describe the existing setup. The bell has two chimes, and
they are metal bars, each about an inch by half a foot. The solenoid is
spring loaded. When the button is pressed, the solenoid is energized,
moving the plunger and causing it to compress the spring and strike one
chime. When the button is released, the spring pushes the plunger back
toward its rest position so as to strike the other chime. Of course the
power is from a transformer, and the switch simply completes the circuit
through the solenoid. As I mentioned before, I measure a steady 12.8
VAC across the solenoid when it is energized (ie, during the time
between the two stikes of the chimes).